1. Field of the Invention
The invention relates generally to systems and devices utilized to minimize the amount of energy required in the performance of a particular task. More specifically, the invention relates to apparatus for the minimization of energy required in the forehearth of a glass furnace. Still more specifically, the invention relates to apparatus for automatically adjusting the amount of cooling wind used in a forehearth.
2. Description of Prior Art
The use of cooling wind or other cooling media in glass making devices is well known for reducing the temperature thereof at a predetermined desirable rate. The term "cooling wind" is used herein in the context of glass forehearths to mean atmospheric air which is blown through a distribution network into a forehearth in order to cool the molten glass in the forehearth at a predetermined rate to produce a gradient temperature distribution in the glass over the length of the forehearth.
In order to understand the disadvantages of the prior art and the problems solved by the present invention, a brief discussion of a prior art forehearth cooling adjustment system will be beneficial. Accordingly, referring now to FIG. 2 there is shown a diagrammatic elevational cross section of a cooling zone of a prior art forehearth including a cooling wind distribution system and a manual mechanism for control thereof. The manual adjustment mechanism is, according to the present invention, replaced by the motor and associated components shown in FIG. 3.
The prior art cooling system shown in FIG. 2 includes a ducting network 400 for the distribution of cooling air blown (by means not shown) into inlet 402 and past butterfly inlet control valve 404. Network 400 causes the cooling air to follow the path shown by arrows 406 and 408 into forehearth chamber 410 above the surface of glass 411 which is heated by burners 413. The cooling air then proceeds through flue 412 and past adjustable refractory outlet damper block 414. The amount of cooling wind passing through forehearth chamber 410 is adjustable and is controlled by the opening of inlet control valve 404 as well as by the gap 416 between outlet damper 414 and flue 412. In the prior art system shown, the openings of control valve 404 and gap 416 are controlled by rotation of a threaded manual adjustment rod 420 secured at 422 to the end of damper lever 424. Rod 420 is moved by rotation of hand nut 425 which is prevented from moving vertically by bracket 426. Damper lever 424 is pivotable about fulcrum 427 so that a vertical adjustment downward of rod 420 will cause a corresponding vertical movement upward of block 414. Simultaneously, control valve 404 will be caused to open a greater amount by movement downward of control rod 428 which is secured at point 430 to lever 424 intermediate fulcrum 427 and the point of attachment 422 of rod 420. The extent of the openings and, therefore, the amount of cooling wind is indicated on scale 421.
Those skilled in the art will understand that the cooling wind distribution system shown in FIG. 2 is one of several similar systems which are spaced apart longitudinally along the length of the cooling zone sections of a forehearth. For example, three such systems may be used in one ten foot long cooling zone and each system may have identical or different cooling wind scale settings, as desired by the operator.
It will be understood that glass forehearths known in the prior art generally utilize either electrical elements or gas-fired (or oil-fired) burners to heat the glass as it flows to, for example, a bottle forming machine. Each of these heating means is automatically thermostatically controlled, for example, by a pyrometer, radiation sensor, etc. (not shown), in order to maintain the glass within a desired predetermined temperature range. Furthermore, those skilled in the art will understand that a glass forehearth generally has two or more longitudinally extending cooling zone sections in which the glass temperature is distributed according to a predetermined gradient (or within a small range of gradients). The simultaneous heating and cooling in the forehearth is used to control the temperature gradient as well as the temperature.
Either gas or electric heating means is automatically operable over a predetermined range from minimum to maximum, the minimum setting being generally the least amount of heating energy sufficient to prevent backfiring of the gas-air pressure burners, or allow control using electric heat, and the maximum setting being the greatest amount of heating energy which may be produced by the heating means. The energy level produced by the heating means at any time is automatically controlled within this range by the thermostatic or other similar sensor.
As shown in FIG. 2, cooling wind is used simultaneously with the application of heat to the molten glass. This simultaneous use of cooling and heating in a forehearth makes it desirable to use the lowest practical amount of cooling wind in order to keep the heating energy at its lowest practical level. However, continual changes in incoming glass temperature, ambient temperature, and humidity necessarily require relatively frequent operator adjustments in the amount of cooling wind in order to enable the automatic temperature control to maintain the glass heating system within a desired low range which is generally very narrow.
An understanding of the manner in which an operator generally controls the amount of cooling wind is helpful in order to understand the prior art.
The operator notes the level of energy being used at any particular point in time in order to heat the glass. Since glass is automatically heated to the proper temperature and automatically maintained at the proper temperature gradient, the operator need not be concerned with adjusting the temperature of the glass but, rather, with controlling the level of energy being utilized to maintain that temperature and gradient. As more energy is being utilized as indicated by, for example, kilowatt meters, the operator would decrease the amount of cooling wind as the energy level is increased. An increased energy level is an indication that too much fuel is unnecessarily being used to maintain the proper temperature range and gradient and, since the cooling wind is in constant opposition to the heating energy, a decrease in the cooling wind would enable the heating energy to be more effective. Thus, a decrease in the cooling wind would enable the same temperature range and gradient to be maintained with a lesser amount of fuel.
Similarly, if a low limit of energy is approached, there is a possibility that the temperature range and gradient of the glass will go out of control because the system generally operates in an automatic mode only above a certain minimum energy level. Thus, the operator would not want the energy level to reach this level and in order to prevent this he would increase the amount of cooling air being used. Since the heating energy cannot go below the minimum level (while maintaining control), the cooling wind must be increased in order to cool the glass and thereby require the heating system to expend additional energy and thereby stay slightly above the minimum energy level.
Since cooling wind adjustments are relatively coarse and have a long response time, the operator's general reaction is to not operate the forehearth near the minimum energy limit. If the operator does not operate near the minimum energy limit he must necessarily keep the cooling wind set higher than would otherwise be required to balance the heating energy to maintain it just above the minimum (automatically controlled) energy limit. This higher cooling wind necessarily means more heat is needlessly required to balance against it to maintain proper glass temperature.
This is especially true prior to periods of an operator's absence, such as nights and weekends when he will not be present to monitor energy usage and prevent the low limit from being passed. While this type of excessive cooling wind setting leaves an extra margin for reduction of heating by the automatic temperature control on the forehearth, it wastes a substantial amount of heating fuel unnecessarily and also requires the use of additional fan motor power to blow the cooling wind.
No prior art is known relating to the minimization of energy usage in the forehearth of a glass furnace. However, prior art automatic systems are known for the temperature control of the glass in a forehearth. One such system is disclosed in the U.S. Pat. No. 3,010,657 dated Nov. 28, 1961. The apparatus disclosed in the '657 patent adjusts the cooling wind in response to a sensed temperature, however, it is unsuitable for the minimization of energy usage. Moreover, the apparatus disclosed in the '657 patent uses a single controller to control both heating and cooling and does not take into account the fact that heating and cooling systems have different response times. The '657 apparatus thus creates an instability because it is difficult to balance or continuously adjust simultaneous heating and cooling in a forehearth.
Another temperature control system known in the prior art is disclosed in U.S. Pat. No. 2,658,687 dated Nov. 10, 1953. The '687 apparatus uses timers for controlling the application of cooling water to cooling air in order to maintain the temperature of glass making equipment within a desired operating range. The '687 apparatus is not suitable to control the cooling wind of forehearths since, inter alia, it only permits positive cooling adjustment in one direction i.e. it only enables the cooling media to be made increasingly colder and relies upon passive heating from the glass making equipment being cooled in order to increase the temperature of the equipment. A cooling wind adjustment system in a forehearth, on the contrary, requires an ability to vary the amount of cooling wind in both directions over a predetermined range in order to compensate for differences in the incoming glass or ambient environment.
One of the disadvantages of prior art forehearth cooling adjustment systems, whether manual or automatic, is their inability to facilitate temperature stabilization within the forehearth. Due to the inherent difference in response time of heating and cooling functions any adjustment system which uses the same controller for controlling the heating and cooling systems will necessarily result in an instability. This makes it difficult to maintain any stable temperature for any reasonable time period and requires constant adjustments of heating and cooling levels.
Furthermore, no prior art system is known which enables automatic forehearth cooling adjustment in order to minimize the amount of energy utilized while still enbling an automatic temperature controller to maintain the material in the forehearth at a predetermined temperature range and gradient.
Accordingly, it is an object of this invention to provide an automatic forehearth cooling adjustment system which does not cause instability of any conventional temperature control system.
It is a further object of this invention to provide an automatic forehearth cooling adjustment system which enables the minimization of energy required to maintain the material in the forehearth at a predetermined temperature and longitudinal gradient.
It is still a further object of this invention to provide an automatic forehearth cooling adjustment system for continually sensing the need for an adjustment in the amount of cooling wind required in order to maintain the temperature of the material in the forehearth accurately controlled by the utilization of as low an amount of energy as practicable.
It is still a further object of this invention to provide an automatic forehearth cooling adjustment system which promptly initiates relatively small changes in the amount of cooling wind as soon as the need for such change is sensed.
It is yet another object of this invention to provide an automatic forehearth cooling adjustment system which enables temperature stabilization within the forehearth during a relatively long period after a change in the amount of cooling wind.